The control of glial differentiation, and the mechanisms of glia-axon interactions and myelination are areas of active investigation. I have previously characterized the oligodendrocyte-myelin glycoprotein (OMgp) in the central nervous system (CNS). The temporal-spatial expression of OMgp correlates with the caudal-rostral axis of CNS myelination. The structure of OMgp provides insight into the mechanisms which underlie this role in CNS myelination. OMgp contains a leucine-rich repeat (LRR) domain, which has been implicated in protein-protein interactions, and its post-translational modifications include a glycosyl-phosphatidylinositol (GPI) attachment. There is growing evidence that the GPI anchor plays a role in activation of tyrosine kinase pathways, which in some cases localizes within caveolar vesicles. Recent observations and our preliminary data indicate that OMgp is present in the peripheral nervous system (PNS), particularly at the paranodal regions of myelin, and is expressed by myelinating Schwann cells. We are interested in OMgp's role in the formation and maintenance of PNS myelin. We speculate that OMgp's expression by myelinating Schwann cells has the same restricted developmental expression as OMgp in the CNS. By virtue of its LRRs and GPI membrane anchor, we hypothesize that OMgp interacts with other polypeptides, such as receptors on axons or other cells and/or free ligands. We believe these interactions will result in tyrosine kinase activation and phosphorylation of downstream pathways important in Schwann cell myelination. The purpose of the current proposal is to characterize OMgp's expression within developing Schwann cells, to identify the molecules which interact with OMgp, to explore the resultant activation of tyrosine kinase pathways, and to examine the effects of transfected mutant forms of OMgp which lack either the LRRs or the GPI anchor on these pathways. We have four specific aims: 1. Determine OMgp expression during peripheral nerve development, 2. Examine in vitro expression of OMgp in Schwann cells, 3. Identify polypeptides which interact with OMgp and characterize the role of OMgp in signal transduction, and 4. Create mutant OMgp constructs which: i) lack the LRR domain, or ii) exist as a transmembrane form and transfect these mutant forms of OMgp into immortalized Schwann cells. Compare the ability of polyclonal anti-OMgp antibodies to induce a myelinating phenotype and/or to activate tyrosine kinase pathways in native vs. mutant OMgp transfected cells.